Bioaerosols consist of biological compounds—mainly cell debris, viruses, bacteria, and fungi—suspended in the air. The cell debris and microbial organisms become aerosolized to form bioaerosols originating from animal respiration, skin, fur, feathers, and manure. Bioaerosols are often present at varying concentrations that are dependent on a number of factors, including emission rates, wind speed, and precipitation. Bioaerosols are thought to be a cause of concern for human health primarily because of the pathogenic viruses and bacteria they may contain. Bioaerosols may be inhaled into the lungs, where they can cause infections and allergic reactions. The people most at risk are farm or plant workers, who are in close proximity to animals and manure for extended periods of time. Aerosolization might occur from animal housing, manure storage, or land to which manure is applied. A recent National Research Council report on the land application of human biosolids found that there is a lack of scientific evidence that human settlements near these land application areas show adverse health effects (NRC, 2002c). That report recommends that the U.S. Environmental Protection agency “conduct studies that examine exposure and potential health risks to workers and community populations” from application of biosolids.
The most pressing issue with regard to bioaerosols is the challenge associated with their measurement and monitoring in the outdoor environment. The difficulty is due in large part to the diversity of organisms that can occur in a given quantity of air. One potential solution to this problem is the use of indicator species. Several technologies and methods exist to accurately measure aerosol emissions. Among these technologies are the aerosol mass spectrometer (ASM) and the electronic nose. Other methods used include bacterial culturing and molecular or chemical techniques.
Reducing the levels of pathogens before they become aerosolized is an option that would reduce bioaerosol pathogenicity. Several different methods can be used to accomplish this: one is to reduce the pathogen levels in the animal through vaccination, antibiotic therapy, diet modification, or on-farm hygiene and sanitation. Other processes focus on the inactivation of pathogens in animal waste. Inactivation of pathogens in manure can be achieved through its conversion to salable fertilizer, which may involve chemical disinfection and composting. The use of lagoons and biofilters may also provide an effective treatment. The treatment techniques that are most effective at reducing pathogen levels may be the most costly, so that reducing these costs will be important. Another important area for study is the impact of bioaerosols from animal operations on human health. Extensive studies have been undertaken on the impacts of bioaerosols and pathogens on human health, but these studies have focused on the indoor environment in places such as offices, hospitals, and animal sheds.
Until further research has been done, conclusions about the health issues surrounding bioaerosols cannot be reached; likewise, conclusions and recommendations concerning bioaerosol emissions cannot be formulated.